1. Field of the Invention
The present invention relates to a system and method for controlling exhaust gas recirculation in a multi-cylinder internal combustion engine.
2. Background Art
The use of exhaust gas recirculation (EGR) to reduce feedgas emissions of nitrogen oxides is well known. The accuracy of various EGR control systems may depend upon proper operation and control of an EGR valve, which may be a proportional or on/off type valve. Various EGR control systems, including both open-loop and closed-loop control systems, have been developed to more accurately control the EGR valve in an attempt to more accurately control EGR flow. Modern internal combustion engine technology employs a wide variety of inlet and outlet airflow control devices to improve engine efficiency and reduce emissions. However, this technology may affect determination of a desired EGR flow and/or actual EGR flow for a particular EGR valve position. For example, electronically controlled throttle valves, charge motion control valves, variable valve timing (VVT), variable cam timing (VCT), and/or variable valve lift control, or any other device which affects the residual exhaust gas within the cylinders may all have an impact on EGR flow control.
A system and method for controlling a multi-cylinder internal combustion engine having at least one automatically controllable airflow actuator and an exhaust gas recirculation (EGR) system including an EGR valve include determining a desired manifold pressure based at least in part on position of the automatically controllable airflow actuator and controlling the EGR valve such that a measured manifold pressure approaches the desired manifold pressure. In one embodiment, the automatically controllable airflow actuators include a charge motion control valve and a variable cam timing device. In other embodiments, the automatically controllable airflow actuators may include variable valve lift devices, variable valve timing devices, or any other device that affects the residual exhaust gases within the cylinders.
The present invention includes a number of advantages. For example, the present invention provides a feedback control system using manifold pressure as a feedback signal. The feedback control automatically corrects all uncertainties introduced by the EGR control valve and any other airflow actuators which affect residual exhaust gases in the cylinders. In addition, the use of a MAP sensor for feedback control provides a higher accuracy than many other engine sensors to further improve the accuracy of delivered exhaust gas.
The above advantage and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.